SUMMARY OF THE INVENTION
The present invention provides compounds of the general formula I ##STR3## where D is the radical of a diazo compound of the aniline series which is free from complex-forming hydroxyl and carboxyl groups, R is hydrogen or an aromatic radical, X is alkyl, a carboxylic acid ester group, unsubstitued or substituted aryl or acylamino, and the ring A may be substituted but is free from SO.sub.3 H groups.